The present invention relates to an elevator supervision method and system which greatly simplify the components used in and the architecture of the safety chain but yet enhance the operating performance of an elevator.
Historically it has been standard practice within the elevator industry to strictly separate the collection of information for safety purposes from that for elevator control purposes. This is partly due to the fact that the elevator controller requires information at high precision and frequency regarding the car's position and speed, whereas the most important factor for the safety chain is that the information supplied to it is guaranteed as fail-safe. Accordingly, while the sensor technology used to supply the controller with information has improved dramatically over recent years, the sensors used in elevator safety chains are still based on relatively old “tried and trusted” mechanical or electromechanical principles with very restricted functionality. The conventional overspeed governor is set to actuate at a single predetermined overspeed value and the collection of safety-relevant positional information is restricted to the hoistway ends and the landing door zones.
Since the controller and the safety chain systems independently gather the same information to a certain extent, there has always been a partial redundancy in the collection of information within existing elevator installations.
There have been proposals to replace components of the safety chain, for example the conventional overspeed governors and the emergency limit switches at the hoistway ends, with more intelligent electronic or programmable sensors. Such a system has been described in WO-A1-03/011733 wherein a single-track of Manchester coding mounted along the entire elevator hoistway is read by sensors mounted on the car and provides the controller with very precise positional information. Furthermore, since it incorporates two identical sensors connected to two mutually supervising processors it fulfils the required parallel redundancy criterion to provide fail-safe safety chain information. However, it will be appreciated that this system is relatively expensive as it necessarily includes a redundant sensor and is therefore more appropriate to high-rise elevator applications than to low and medium-rise installations. Furthermore, since identical sensors are used to measure the same parameter it is inherent that they are more likely to fail at approximately the same time since they are susceptible to the same manufacturing tolerances and operating conditions.